hungerford: aquatic hemiptera. 199 



Key to Ambrysus — continued. 



BB. Head very sensibly narrower, including the eyes, less than 

 half the width of the pronotum behind. Pronotum with a 

 slight depression, sometimes very superficial, wrinkled trans- 

 versely on the middle of the anterior border. 

 C. Coloration darker, segments of connexivum darkened 

 with posterior angle a little prominent. A. pudicus. 

 CC. Coloration lighter, segments of connexivum not as above. 



A. circumcinctus. 

 AA. Pronotum densely punctate, especially laterally. 



B. Size small, below 8 mm. Median depression of the anterior 

 margin of the pronotum feeble, transversely wrinkled. 

 Color "claire." Width of the head, including eyes, a little 

 less than half the width of the pronotum behind. Eyes con- 

 verging in front. Length, 7.2 mm.; width, 4.5 mm. 



A. calif (yi'nicus. 

 BB. Size larger, above 9 mm. in length. 



C. Anterior margin of pronotum very visibly "reborde" 

 (with a visible ledge) behind the eyes; depression of the 

 middle of the anterior margin transversely wrinkled and 

 punctate between the wrinkles ; interocular portion of the 

 head narrowed in front; head with a very feeble longi- 

 tudinal depression forming a median furrow, plainer 

 behind. Length, 11.8 mm; width, 6.7 mm. 



A. melanoyterus. 

 CC. Anterior margin of pronotum not or slightly visibly 

 ledged (boi'dered) and then only in the middle. 

 D. Anterior angles of pronotum very prominent, 

 sharp. 

 E. Average size larger (9.3 to 10.6 mm.) ; lateral 

 sides of pronotum more dilated and more 

 strongly arcuate without, dilation of embol- 

 ium more pronounced. Coloration pale. 



A. marmon. 

 EE. Average size smaller (8.6 to 10 mm.) ; lat- 

 eral sides of pronotum less dilated and less 

 strongly arcuate without; dilation of embol- 

 ium less pronounced. Coloration deeper. 

 A heidenianni 

 DD. Anterior angles of pronotum less prominent, almost 

 right angles, scarcely pointed. 

 E. Head narrow, as long as the width of the in- 

 terocular space behind; length of the head 

 and pronotum together a little greater than 

 half the greatest width of the pronotum. 



A. pioicticollis. 

 EE. Head wide, length of the head and pronotum 

 together equal to or a little less than half the 

 greatest width of the pronotum. Pronotum 



